Imaging and Signalling | OCR A-Level Physics B (Advancing Physics) (H557)
Imaging and Signalling
- 170 questions
- 12 subtopics
- The physics content, examined on all three papers
- Component 01, Component 02 and Component 03
Imaging and Signalling is examined in all three written papers — the specification states that Components 01, 02 and 03 each assess content from across all the teaching modules, so nothing is confined to one paper.
It covers real images and the curvature of wave-fronts, lens power and focal length, the thin lens equation and the Cartesian convention, linear magnification, measuring the power and focal length of a converging lens, images as arrays of numbers, bits, bytes and the information in an image, Enhancing a digital image, wave-forms, frequency and wave speed, sampling and digitising an analogue signal, noise, resolution and digital transmission and polarisation of electromagnetic waves.
Sample questions from Imaging and Signalling
Answer each one closed book first, then open the answer.
-
Real images and the curvature of wave-fronts
Explain why the curvature added by a given thin lens is the same wherever the object is placed.
Show the answer
The curvature added depends only on the shape of the lens surfaces and its refractive index, neither of which changes when the object moves. -
Lens power and focal length
A wave-front diverging with a curvature of 2.0 m⁻¹ reaches a +5.0 D lens. Describe the wave-front that leaves.
Show the answer
The lens adds 5.0 m⁻¹ of curvature, so the wave-front leaves converging with a curvature of 3.0 m⁻¹ and comes to a focus 0.33 m beyond the lens. -
Linear magnification
An object 0.30 m in front of a lens gives an image 0.60 m beyond it. Calculate the magnification and describe the image.
Show the answer
m = 0.60/(−0.30) = −2.0, so the image is real, inverted and twice the height of the object. -
Measuring the power and focal length of a converging lens
Why should the illuminated object, the lens and the screen all be set at the same height?
Show the answer
The image then forms on the axis of the lens, which avoids distortion and makes the sharp position easier to identify. -
Bits, bytes and the information in an image
State the relationship giving the number of bits needed to represent N alternatives.
Show the answer
b = log₂N. -
Enhancing a digital image
Explain why no amount of processing can add information that was not captured.
Show the answer
Processing only recombines the numbers already stored, so detail smaller than a pixel or buried in the noise was never recorded and cannot be recovered. -
Sampling and digitising an analogue signal
A range of 5.0 V is digitised using 8 bits. Calculate the resolution.
Show the answer
There are 256 levels, so the resolution is 5.0/256 = 0.020 V, about 20 mV. -
Noise, resolution and digital transmission
A signal is sampled 20 000 times per second. State the highest signal frequency that can be faithfully recorded.
Show the answer
Just under 10 kHz, which is half the sampling rate.
The 12 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Real images and the curvature of wave-fronts | Recall questions on defining wave-front curvature, the fixed amount a thin lens adds, wave-fronts from a distant object, the standard ray constructions, and why the image is inverted. | 14 |
| Lens power and focal length | Recall questions on lens power P = 1/f and the dioptre, converting between power and focal length, the positive power of a converging lens, the thin lens relationship in curvature form, adding the powers of lenses in contact, why opticians use dioptres, the curvature a lens adds to a wave-front, and how refractive index and surrounding water change power. | 14 |
| The thin lens equation and the Cartesian convention | Recall questions on the sign convention for object and image distances, calculating image position, focal length and power, the least possible object–image separation, and covering half a lens. | 15 |
| Linear magnification | Recall questions on relating magnification to object and image distances, why it has no unit, what a negative value means, image heights in cameras and projectors, and distant objects. | 12 |
| Measuring the power and focal length of a converging lens | Recall questions on the distant-object estimate, the illuminated-object and screen method, plotting reciprocal distances, locating the sharpest image, systematic error in the distances, and testing a very weak lens. | 15 |
| Images as arrays of numbers | Recall questions on pixels, bits and bytes, greyscale images as arrays of numbers, grey levels and bits per pixel, image resolution and pixel size, why stored numbers allow processing, false colour and thermal images, noise, and the bits needed for colour and 24-bit images. | 15 |
| Bits, bytes and the information in an image | Recall questions on image information from pixels and bits per pixel, converting to bytes, the alternatives and grey levels a number of bits gives, logarithms to base two, and coarse quantisation. | 14 |
| Enhancing a digital image | Recall questions on changing brightness and contrast by adding to and multiplying pixel values, saturation, smoothing to reduce noise and its cost, median filters, edge detection, why processing cannot add information, false colour and raised contrast in medical images, and repeated smoothing. | 13 |
| Wave-forms, frequency and wave speed | Recall questions on reading the period and amplitude from a wave-form, f = 1/T, v = fλ for radio waves and ultrasound, how wavelength limits the detail of an ultrasound scan, peak-to-peak voltage, and the wave-forms of pure and noisy signals. | 13 |
| Sampling and digitising an analogue signal | Recall questions on analogue and digital signals, sampling and turning samples into binary numbers, the resolution of a digitisation, the minimum sampling rate and what goes wrong below it, filtering before digitising, the staircase shape and how bits and sampling rate change it, sampling music 44 100 times per second, and quantisation error. | 16 |
| Noise, resolution and digital transmission | Recall questions on noise and the limit it sets on useful bits, b = log₂(Vₜₒₜₐₗ/Vₙₒᵢₛₑ) and why it is rounded down, rate of transmission as samples per second × bits per sample, the highest frequency a sampling rate can record, the advantages and disadvantages of digital transmission, and regenerating pulses before noise grows too large. | 15 |
| Polarisation of electromagnetic waves | Recall questions on plane polarisation and why only transverse waves show it, polarising filters, rotating one of two filters and crossed polarisers, demonstrating polarisation with microwaves and a metal grille, unpolarised lamp light, polarising sunglasses, stressed plastic between crossed polarisers, and liquid crystal displays. | 14 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
-
Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
-
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
-
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics B (Advancing Physics) Active Recall Guide
Every topic, not just this one. 2,455 questions with their answers.